1. Field of the Invention
The present invention relates to a driving circuit for a single-phase brushless motor.
2. Description of the Related Art
A brushless motor among DC motors has advantages such as its long life since it does not use any brush or commutator. By employing a single-phase brushless motor disclosed in Japanese Laid-Open Patent Publication No. 2008-312440, for example, only one position detecting device such as a Hall element is sufficient, a single phase is also sufficient in the driving circuit, and thus cost and size, etc., can be reduced.
Whereas, in a common single-phase brushless motor, a stop position exists which is referred to as “dead (locked) point” at which a rotor (rotator) thereof does not rotate even when a driving current starts to be supplied to a driving coil thereof. Thus, the single-phase brushless motor in Japanese Laid-Open Patent Publication No. 2008-312440 takes countermeasures to prevent the dead point by stopping at a position where the center of permanent magnets thereof and the center of the driving coil are deviated from each other. Further, a driving control circuit is also disclosed therein that applies a voltage generating a current in the direction opposite to that of an induced voltage (counter electromotive voltage) generated across the driving coil, thereby realizing improvement in efficiency, reduction in vibration and noise, etc.
As such, taking the countermeasures against the dead point and using the techniques to reduce vibration and noise as above enable the single-phase brushless motor to be used in various uses such as a fan motor.
Since the single-phase brushless motor is able to be configured to be small in size at a low cost, a suitable use may be a vibration motor used for a vibration function of a cellular telephone to let a user know arrival of a call, for example. Especially, when it is used as the vibration motor, a rectangular wave, more likely to generate vibrations, may be used as a driving signal, and thus the motor driving circuit can be reduced in a circuit scale, and a motor driving IC can be reduced in cost and size.
Further, among motor driving ICs, a motor driving IC is also known that incorporates therein a Hall element to detect a rotation position of a rotor. However, since such a Hall-element-incorporating IC needs to be mounted in the interior of the motor, the effect of the miniaturization thereof is reduced. Further, since an error arises in the precision for detecting the rotation position of the rotor due to characteristics of the Hall element itself during the manufacture of the IC, a test to apply a magnetic field is required before shipment of the motor. Thus, the effect achieved by the cost reduction is reduced.